Pattayam based on false document

Dear Sir, First of all thank you for your time to answer my question. let me explain the question Party A & B are brother and sister Parent of A & B gave a property X to party A through a registered will Z Party B died , and his heirs created a partition deed including property X , which actually as belong to party A as per registered will Z not the party B. the document the heirs created have same back document Z , so upon cross checking the document Z its evident that heirs of party B wrongly include X to their partition deed. the person who took the X , applied for pattayam , and he got it somehow 20 years ago and he built a house and he is living on it. at the time the person A was tool old and she was not directly managing any property around 85 years old, and even before that party B and their heirs were looking after the property as property located in the home town. party A died at the age of 98 and only after that heirs of party A realized that heirs of party B made a falsely included the property X in their partition deed and make pattayam for it. is there any chance for us? as its around 20 years delay some says there is some rule which says after certain time of possession the land is theirs. they actually cheated us can we file cheating case or forgery case on party B heirs.